Strength test method for anchor installed underwater and floating body

ABSTRACT

A simplified structure allows inspection of the installation strength of an anchor installed underwater. A method includes applying, to an anchor, a lifting force from above a floating body floating on a water surface to submerge the floating body into water, and setting a volume of submergence by which the floating body is submerged to a value to produce a lifting force corresponding to a predetermined installation strength and determining whether the anchor is immovable. The volume of submergence by which the floating body is submerged to produce the lifting force corresponding to the predetermined installation strength is calculated based on the buoyancy acting on the floating body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International PatentApplication No. PCT/JP2018/016556 filed on Apr. 24, 2018, the entirecontent of which is incorporated by reference.

BACKGROUND OF INVENTION Field of the Invention

The present invention relates to a strength test method for an anchorinstalled underwater for testing whether an anchor for various mooringtargets, such as floating photovoltaic power systems, aquaculture cages,floating piers, and water sports facilities, has an intended tensilestrength.

Background Art

A method for inspecting the installation state of an anchor is describedin Patent Literature 1.

This inspection method includes lifting a rod of an installed anchorwith a hollow hydraulic jack and determining whether a load indicated bya hydraulic gauge reaches an intended resistance against pulling. Thehydraulic jack is included in a lifting structure placed at the waterbottom under a floating platform.

The method uses large equipment for inspection, including the liftingstructure placed at the water bottom, in addition to the floatingplatform, and further a holder for the hollow hydraulic jack in thelifting structure.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 6252882

SUMMARY OF INVENTION Technical Problem

One or more aspects of the present invention are directed to asimplified structure for inspecting an anchor.

Solution to Problem

A strength test method for an anchor installed underwater includesapplying, to an anchor installed underwater, a lifting force from abovea floating body floating on a water surface to submerge the floatingbody into water, and setting a volume of submergence by which thefloating body is submerged to a value to produce a lifting forcecorresponding to a predetermined installation strength and determiningwhether the anchor is immovable.

The volume by which the floating body is submerged to produce thelifting force corresponding to the predetermined installation strengthis calculated based on the buoyancy acting on the floating body.

In the structure, the anchor is pulled from above the floating body tosubmerge a portion of the floating body exposed above the water surfaceinto the water and to apply the lifting force corresponding to thepredetermined installation strength to the anchor. When the anchorremains installed, the anchor is determined to have the installationstrength. When the anchor fails to remain installed, the anchor isdetermined to lack the strength. The anchor lacking the strength ispulled up, thus readily moving the floating body and revealinginsufficient installation of the anchor.

Advantageous Effects

The method according to the above aspect of the present inventionenables the inspection with a simple operation of pulling the installedanchor from above the floating body to submerge the floating body by apredetermined volume into the water. The structure simply includes atleast the floating body and a device for determining the volume by whichthe floating body is submerged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram describing a strength test method for an anchorinstalled underwater.

FIG. 2 is a perspective view of a floating body.

FIG. 3 is a diagram describing a depth of submergence and a volume ofsubmergence.

FIG. 4 is a diagram describing a method for installing an anchor.

DETAILED DESCRIPTION

One embodiment of the present invention will now be described withreference to the drawings.

FIG. 1 is a diagram describing a strength test method for an anchorinstalled underwater. The test method includes applying, to an anchor 11installed underwater by embedding or driving, a lifting force or avertically upward force from above a floating body 13 floating on awater surface 12 to submerge the floating body 13 into the water. Theamount or the volume of submergence is set to a value to produce alifting force corresponding to an intended installation strength. Themethod then determines whether the anchor 11 is immovable. Whenimmovable, the anchor 11 passes the test. When moved in the pullingdirection, the anchor 11 fails the test.

The test method uses the floating body 13. The floating body 13 floatson the water. More specifically, the floating body 13 has a bottomsurface submerged in the water and an upper portion including the uppersurface exposed above the water surface. When the predetermined pullingforce described above is applied to the anchor 11 from above, thefloating body 13 with buoyancy does not entirely become submerged in thewater.

FIG. 2 is a perspective view of an example of the floating body 13. Thefloating body 13 is a thick polystyrene board that is square in a planview. The floating body 13 includes a polystyrene floating board 31 anda hard protective metal plate 32 on the upper surface of the floatingboard 31. The floating board 31 is solid and includes thick polystyreneboards combined together.

The floating body 13 includes gauges 33 to indicate the depth or thevolume by which the floating body 13 is submerged in the water. Thegauges 33 indicating the depth of submergence can be simpler.

The gauges 33 shown in FIG. 2 are scale plates 34 including scale marksindicating the length (height) of the floating body 13 in the verticaldirection, or more specifically, in the thickness direction. The scaleplates 34 may be fixed at appropriate positions or, for example, at thefour corners. The scale plates 34 at such positions are easily viewableand can protect the corners of the floating body 13 when formed from ahard material.

Referring now to FIG. 3, the volume by which the floating body 13 issubmerged to produce a lifting force corresponding to an intendedinstallation strength will now be described.

The buoyancy acting on the floating body 13 is ρVg (N), where g (m/s²)is a gravitational acceleration, ρ (kg/m³) is the density of water, andV (m³) is the volume of a portion of the floating body 13 submergedbelow the water surface 12.

The floating body 13 having a mass m (kg) is also under a gravitationalforce with a magnitude mg (N), which is balanced with the buoyancy(ρVg=mg). Thus, the volume V of the portion submerged in the water is

V=m/ρ,

indicating that the floating body 13 is submerged in the water by m/ρ(m³).

Buoyancy is proportional to the volume of a submerged portion in thewater. Thus, a volume V1 (m³) by which the floating body 13 is to besubmerged to produce a lifting force corresponding to an intendedinstallation strength is obtained. With this volume of submergence andthe dimensions of the floating body 13, a depth H of submergence for thefloating body 13 is obtained as, for example, 10 cm for producing alifting force of 2 t (ton).

For the floating body 13, a machine is used to pull the anchor 11installed underwater. As indicated by the imaginary lines in FIG. 1, theanchor 11 is pulled by a construction machine 15, such as a hydraulicexcavator. The construction machine 15 in use has a piling attachment 16attached to the distal end of the arm.

As shown in FIG. 4, the construction machine 15 with the pilingattachment 16 is also used to drive or embed the anchor 11. The floatingbody 13 is used as a working platform 17 for placing the constructionmachine 15 on the water. In other words, the floating body 13 used forthe strength test also serves as the working platform 17 for installingthe anchor 11.

The installation strength test for the anchor 11 using the floating body13 and the construction machine 15 is performed consecutively to theinstallation of the anchor 11.

More specifically, the construction machine 15 is placed on the floatingbody 13 used as the working platform 17, and the floating body 13 istowed to a site on the water under which the anchor is to be installed.At the site, the construction machine 15 holds the upper end of theanchor 11 and drives the anchor 11 into a water bottom 18 as shown inFIG. 4. This completes the installation of the anchor 11.

While holding the upper end of the anchor 11, the construction machine15 subsequently pulls the anchor 11. The anchor 11 driven into the waterbottom 18 is not easily pulled out. As indicated by the solid lines inFIG. 1, the portion of the floating body 13 exposed above the watersurface 12 is submerged into the water.

The volume to be submerged by pulling is set to a value for producingthe predetermined lifting force described above. The volume by which thefloating body 13 is submerged is determined with the gauges 33 includedin the floating body 13.

More specifically, the position of the water surface 12 before thesubmergence is determined with the scale plates 34 serving as the gauges33. For example, when a depth of submergence of 10 cm produces a liftingforce of 2 t, which corresponds to the intended installation strength, alifting force is applied to the anchor 11 until the floating body 13 issubmerged 10 cm deeper from the yet submerged water surface 12. Thescale plates 34 may be checked from above the floating body 13 or may bechecked by a diver entering the water for installing the anchor 11.

Although the floating body 13 may be inclined by a lifting force appliedto the anchor 11, the scale plates 34, having the scale marks at thefour corners indicating the depth of submergence, allow determination ofthe submergence depth at each corner. This allows easy calculation ofthe predetermined volume of submergence.

After the depth of submergence reaches a predetermined depth, thefloating body 13 retains the state for a predetermined duration. Inother words, the floating body 13 retains the state of being submergedby the predetermined volume. The duration is determined as appropriatein accordance with, for example, the use of the anchor 11, an intendedinstallation strength, and an underwater environment. The duration isnot excessively long and may be several to ten and several minutes, ormore specifically about five minutes, to demonstrate the intendedinstallation strength.

When the anchor 11 remains immovable after being pulled for theduration, the anchor 11 passes the test. When the anchor 11 is lifted,the anchor 11 fails the test and is reinstalled immediately. The anchor11 installed improperly is lifted, allowing the diver working underwaterto notice the movement. The operator operating the construction machine15 also readily senses the movement, rather than with the digitalnumbers indicated on the machine.

As described above, the inspection includes the simple operation ofpulling the anchor 11 from above the floating body 13 to submerge thefloating body 13 in the water by a predetermined volume. The volume bywhich the floating body 13 is submerged is determined with the gauges 33included in the floating body 13. The operation includes simply pullingthe anchor 11 while checking the gauges 33, and is easy.

The operation uses the floating body 13 including the gauges 33. Theanchor 11 is pulled with the construction machine 15 as described above.The floating body 13 eliminates a fixed, dedicated machine (not shown)for pulling the anchor 11. The floating body 13 can thus have a simplerstructure, simplifying the entire equipment for the test.

In particular, the floating body 13 also serves as the working platform17 for installing the anchor 11, further simplifying the entireequipment.

The installation of the anchor 11 and the test on the installationstrength are performed consecutively. This increases the operationefficiency, and provides higher reliability in determining theinstallation strength than in the inspection performed a predeterminedtime after the installation.

The reliability is further increased by retaining the submerged state ofthe floating body 13 for a duration in the installation strength test,after simply submerging the floating body 13 by the predeterminedvolume.

The structure described above is one example for implementing thepresent invention. The present invention is not limited to the structuredescribed above and may include other structures.

The gauges 33 may include, rather than scale marks for indicating thedepth of submergence as described above, other components including afloat on the water surface 12 to allow determination of the depth of theactual submergence with a sense rather than with scale marks. The gauges33 may also include a member that indicates the portion submerged in thewater by changing its appearance.

REFERENCE SIGNS LIST

-   -   11 anchor    -   12 water surface    -   13 floating body    -   17 working platform    -   33 gauge

1. A strength test method for an anchor installed underwater, the methodcomprising: applying, to an anchor installed underwater, a lifting forcefrom above a floating body floating on a water surface to submerge thefloating body into water; and setting a volume of submergence by whichthe floating body is submerged to a value to produce a lifting forcecorresponding to a predetermined installation strength and determiningwhether the anchor is immovable.
 2. The strength test method accordingto claim 1, further comprising: retaining the floating body beingsubmerged by the volume of submergence having the set value.
 3. Thestrength test method according to claim 1, further comprising:determining the volume of submergence by which the floating body issubmerged with a gauge included in the floating body.
 4. The strengthtest method according to claim 1, wherein the floating body includes aworking platform used to install the anchor.
 5. A floating bodyconfigured to float on a water surface to conduct an installationstrength test for an anchor installed underwater, the floating bodycomprising: a gauge configured to indicate a depth or a volume by whichthe floating body is submerged in water.
 6. The floating body accordingto claim 5, wherein the floating body comprises polystyrene.